Implementation of a microcanonical variational transition state theory for direct dynamics calculations of rate constants

An implementation of the variational quantum RRKM program is presented to utilize the direct ab initio dynamics approach for calculating k(E, J), k(E) and k(T) within the framework of the microcanonical transition state (μTST) and microcanonical variational TST (μVT) theories. An algorithm including tunneling contributions in Beyer-Swinehart method for calculating microcanonical rate constants is also proposed. An efficient piece-wise interpolation method is developed to evaluate the Boltzmann integral in calculation of thermal rate constants. Calculations on several test reactions, namely the H(D)2CO→H(D)2 + CO, CH2CO→CH2 + CO and CH4 + H→CH3 + H2 reactions, show that the results are in good agreement with the previous rate constants calculations. This approach would require much less computational resource.